This application will test the hypothesis that granulocyte-macrophage-colony stimulating alveolar macrophage (AM) innate antiviral mechanisms and by limiting inflammation during viral lung infection. GM is a hematopoietic growth factor recently shown to be vital to lung homeostasis and host defense. The role of GM in early hematopoiesis appears to be redundant, however, its role in the lung is unique. While the mechanism(s) through which GM regulates lung host defense are unclear, GM modulates multiple, diverse function of AM. Based on our preliminary data and published reports, we propose that GM interacts with AM precursors in the lung, stimulating their terminal differentiation, and increases their capacity to internalize and degrade viral pathogens from the respiratory surface (i.e., GM increases intrinsic clearance of AM (ICAM). By increasing ICAM, GM increases primary pathogen clearance (i.e., by resident AM) thus reducing or obviating the need for chemotactic/proinflammatory cytokine signaling and secondary clearance (i.e., by recruited leukocytes). Murine models will be used in which the synthesis of GM is: 1) normal (GM+/+; 2) absent (GM-/-); 3) constitutively over- expressed in the lung (SPC-GM/GM-/-); or 4) conditionally expressed in the lung under positive external control using a novel bitransgenic system (BTx-GM or BTx-GM/GM-/-. In the latter model, GM expression can be induced or extinguished, temporally, by addition or withdrawal of oral, aqueous doxycycline resulting in lung GM levels ranging from absence to overexpression. GM-deficient and replete mice will be used to study the in vivo role of GM in: (Aim 1) stimulating AM receptor expression and internalization of adenovirus; (Aim 2) trafficking and degradation of adenovirus in AM; and (Aim 3) limitation of inflammation during adenovirus infection of the respiratory tract. We will identify and characterize the mechanisms by which AM internalize and degrade adenovirus in vivo and in vitro. We will also discern the temporal relationship between GM expression in the lung and AM differentiation, ICAM (for adeno-virus), and the relationship between ICAM and limitation of lung inflammation. Our studies will help clarify the critical role of GM in modulating AM function, stimulation of innate lung host defense, and in limitation of lung inflammation and thus, will help establish the feasibility of the therapeutic use of recombinant GM for prevention or treatment of common acute and chronic lung infection and lung inflammation in various clinical disorders.